NFL free agents usually spend their team visits being told they’re the man. Matt Cassel came to Minnesota and was told in no uncertain terms that he definitely is not the man. But Cassel, a starting quarterback for the past five years, said he accepted the role as Christian Ponder’s backup, calling the Vikings “a perfect fit” when he spoke with the media a day after his signing. “I understand the role completely,” Cassel said Friday. “Without a doubt.” The Vikings weren’t going to sign anyone who couldn’t convince them of that. Since selecting Ponder 12th overall in the 2011 draft, General Manager Rick Spielman and coach Leslie Frazier have been extremely careful not to waver in their support of Ponder, who has struggled at times while posting a 12-14 record and a completion percentage below 60 percent (59.2). On the other hand, the Vikings also weren’t going to stand pat with inexperienced Joe Webb as their backup. Not after Webb stepped in for the injured Ponder and completed just 11 of 30 passes in a 24-10 playoff loss at Green Bay. So within hours of Cassel’s release in Kansas City on Thursday, the Vikings pounced and came away with an eight-year veteran with 62 NFL starts and a reputation for being a well-prepared backup. When the 2008 season began, Cassel was a three-year veteran who never had started a game as Tom Brady’s backup in New England. But in the season opener against Kansas City, Brady went down because of a season-ending knee injury.